1. Field of the Invention
The present invention relates to a method for adjusting a lens offset of a video camera, and particularly to an improved method for adjusting a lens offset capable of advantageously adjusting the offset value of the lens through small travel of a focus lens and a zoom lens.
2. Description of the Conventional Art
Referring to FIG. 1, there is shown a block diagram of a conventional video camera. As shown in the drawing, the conventional video camera includes a lens group 10 having a focus lens and a zoom lens; an iris 20 for controlling the light quantity incident from the lens group 10; a vidicon 30 for forming an optical image of an object incident through the iris 20 and convening the image into multiplexed chrominance signals; a .sampling and gain control unit 40 for dividing the multiplexed chrominance signals outputted from the vidicon 30 into luminance signals and color signals, and controlling the gains thereof; a video signal processing unit 50 for encoding the luminance signals and the color signals outputted from the sampling and gain control unit 40 and outputting composite video signals; a focus evaluation calculating unit 60 for receiving the luminance signals outputted from the sampling and gain control unit 40 and calculating the focus evaluation corresponding to a region of the screen; and a key input unit 100 for selectively inputting the general operations of the video camera. The conventional video camera further includes a microprocessor 70 for adjusting the offset value of the lens according to the key data selected in the key input unit 100 and according to the evaluation value outputted from the focus evaluation calculating unit 6, and performing the control operation; a motor driving unit 80 for driving the lens group 10 according to the control signals of the microprocessor 70; and an iris driving unit 90 for controlling the opening amount of the iris 20.
Referring to the drawings, the operation of the conventional video camera with the above-described construction will be explained.
First, as shown in FIG. 1, when an optical image of an object is incident upon the vidicon 30 through the lens group 10 and the iris 20, the vidicon 30 forms an optical image of the object and outputs the image after converting it into the multiplexed chrominance signals.
Next, the sampling and gain control unit 40 receives the multiplexed signals outputted from the vidicon 30, and divides the signals into luminance signals and color signals. After signal division, the sampling and gain control unit 4 controls the gains thereof and outputs them to the video signal processing unit 50. The luminance signals and the color signals received by the video signal processing unit 50 are encoded into a composite video signal and outputted.
The focus evaluation calculating unit 60 receives the luminance signals from the sampling and gain control unit 40, and calculates the focus evaluation by detecting the amount of the high frequency component of the luminance signals within a region of the image. After calculation, the focus evaluation calculating unit 60 outputs the focus evaluation values to the microprocessor 70.
That is, if the focus is correctly adjusted, the high frequency component of the luminance signal reaches its maximum (the focus evaluation is large), while, if the focus is not correctly adjusted, the high frequency component of the luminance signals becomes small (the focus evaluation is small).
Therefore, the microprocessor 70 receives the focus evaluation values outputted from the focus evaluation calculation unit 60, and controls the motor driving unit 80 to perform an auto-focusing operation.
At this time, when a user pushes the function key through the key input unit 100, the microprocessor 70 calculates the offset value by comparing the theoretical trace curve of FIG. 2 set by the predetermined lens spec values Wx, Wy, Tx and Ty with the actual trace curve formed by moving the positions of the zoom lens and the focus lens, and controls the offset of the lens group 10.
Referring to FIGS. 3 and 4, the method for calculating the offset values of the focus lens and the zoom lens will now be described in detail.
First, when a user pushes the zoom key through the key input unit 100, the microprocessor 70 moves the position of the zoom lens of the lens group 10 by as much as the theoretical value Wx away from a start point, by driving the motor driving unit 80 (step 102).
Next, the microprocessor 70 drives the motor driving unit 80 and moves the position of the focus lens of the lens group 10 away from the start point. And then, the microprocessor 70 seeks the focusing position and stores the position as the first position f1 of the focus lens (step 104).
Thereafter, the microprocessor 70 drives the motor driving unit to move the position of the focus lens of the lens group 10 by as much as the theoretical value Ty toward the start point by driving the motor driving unit 80 (step 106). Again, the microprocessor 70 seeks the focusing position by moving the position of the zoom lens from that position toward the long-distance position and stores the focusing position as the first position z1 of the zoom lens (step 108).
After moving the position of the zoom lens by as much as the theoretical value Tx toward the start point (step 110), the microprocessor 70 moves the position of the focus lens toward the long-distance position, seeks the focusing position, and stores the position as the second position f2 of the focus lens (step 112).
As shown above, when the first and second positions f1 and f2 of the focus lens are obtained, the microprocessor 70 calculates an absolute value by subtracting the value of the second position f2 from the value of the first position f1. The obtained absolute value is compared with the predetermined threshold value (step 114).
If the calculated absolute value is larger than a threshold value, the microprocessor 70 stores the value of the second position f2 of the focus lens as the value of the first position f1 of the focus lens (step 116), and repeatedly performs the operations after step 104. Whereas, if the calculated absolute value is smaller than the threshold value, the microprocessor 70 compares the first and second positions f1 and f2 of the focus lens and the position of the zoom lens, which are calculated from the actual trace curve E, with the data detected from the theoretical trace curve A, and calculates the offset value (step 118).
However, the conventional method for adjusting the lens offset of the conventional video camera has disadvantages, in that it takes much time to calculate the offset value due to much travel of the focus lens and the zoom lens, and errors are easily committed as the motor for driving the focus lens and the zoom lens is frequently driven.